1. Field of the Invention
The present invention relates to power management of a computer.
2. Related Art
According to a conventional power management method, power management is usually performed by individual devices or by individual device groups. The primary control object is a CPU, an LCD or an HDD, and conventionally the following power management methods are performed.
(a) CPU
Generally, it is possible to reduce the amount of power consumption by reducing the speed of the performance (clock frequency). A mode for halting an internal clock (such as stop-grant mode in Pentium), or internal and external clocks (such as stop-clock mode in Pentium) of a CPU has been prepared for the Pentium (a trademark of Intel Corp.) processor, etc. To reduce power consumption, a slow-clock emulation for reducing the clock frequency is performed by halting the clock for a specific period of time. An OS supporting APM (Advanced Power Management) monitors the dispatched state of a task, and halts the clock of the CPU when the OS determines no task is to be executed.
(b) LCD
The ratio of energy consumed by an LCD panel to the total of the required energy is relatively large, and reducing the luminance is a very effective power saving method. It should be noted, however, that generally there is a deterioration in usability when the luminance is reduced. A method is frequently employed whereby the input state of a keyboard is monitored, and the LCD is turned off when it is determined there is no keyboard operation by a user.
(c) HDD
Since a hard disk is not accessed constantly, the halt of the rotation of the disk when there is no disk access is a very effective power saving method. Generally, a method for halting the rotation of the disk is employed when no disk access has occurred for a period of time set by a timer. It should be noted, however, that if the disk has been halted when accessing to the disk, a large amount of power is required for spin-up to activate the disk, and an actual disk access will be delayed. It is, therefore, difficult to appropriately set the above function when frequent disk accesses are required.
The above described power management process for individual devices, or for individual device groups has the following problems: (1) the setting of a parameter for power management is fixed, regardless of the job type that represents the job status of the entire system, including that of present running application programs. Once the value of the parameter has been set, the specified value is usually not changed until the value is specified again. Some notebook computers have control programs that temporarily change the value of the parameter when an event occurs. However, this change is based merely on the usage history of an individual device, and the value of the parameter is not varied in accordance with the job type. (2) the conventional power management method is not flexible because the control of power savings for individual devices is performed completely independently. Although the power consumed by individual devices can be reduced, the total power reduction in a device assembly is not taken into account. Therefore, as a result, an unwanted deterioration of the performance and useability in a specific job type occurs.
As a power management procedure for the entire system, a method whereby, when a specific event occurs, the system shifts between states, such as a normal state, a rest state, a standby state, and a suspend state is disclosed in Japanese Unexamined Patent Publications Nos. Hei 8-36445, 7-302133 and 7-044286. In these publications, the type of application being executed is not taken into account, and the state transition is performed based merely on one predefined device usage status or on an event caused by it, and the control of the device is executed in response to the state transition. The type of application being executed is not taken into account because the methods described in the publications are based on the theory that the system is in the normal state so long as an application program is being executed, and it is therefore assumed that in such a case, the performance of the power saving process either not is required or will result in the occurrence of a problem. Thus, no state transition occurring during the execution of the application program is described in the above publications. Furthermore, the described methods provide the normal state and the suspend state and etc. only for the power reduction. But, no explanation is given for a viewpoint in which by performing power management which increases the power consumption in a job type, the power over long range time period will be reduced.